I think there's a spell in the spell compendium, 'weapon shift' or something like that. It's a 1st level spell. I convinced my GM to let me create a magic item -- a pendant on a cord, that you could wrap around a weapon. It would let you use weapon shift at will as a standard action, although only into 3 different forms. He charged me 2000 gp for it, and so I had either an adamantine greatsword, or an adamantine spiked chain, or an adamantine shortsword. Good for close melee, melee reach, and grappling.